Plant pests, including plant-parasitic nematodes, are a major factor in the loss of the world's agricultural crops. Agriculturally significant nematodes include the sedentary endoparasites, such as those found in the genera Meloidogyne (root-knot nematodes), Heterodera, and Globedera (cyst nematodes).
Currently, plant-parasitic nematodes are generally controlled by chemical nematicides, crop rotation, and growing resistant cultivars. The use of chemical nematicides, however, increases costs to farmers and can cause harmful effects on the ecosystem. Moreover, consumers and government regulators alike are becoming increasingly concerned with the environmental hazards associated with the production and use of synthetic agrochemicals. Traditional breeding methods can be used to select resistant cultivars, but the methods are time-consuming and require continuous effort to maintain disease resistance. See, for example, Grover and Gowthaman (2003) Curr. Sci. 84:330-340. Thus, there is substantial interest in developing novel alternatives for the control of plant pathogens that possess a lower risk of pollution and environmental hazards than is characteristic of traditional agrochemical-based methods and that are less cumbersome than conventional breeding techniques.
A number of biotechnology-based strategies, including disruption of the feeding structure of the nematodes by localized expression of phytotoxic gene product(s) have been investigated, but none of them have reached commercial success. Nevertheless, biological control of plant pests of agricultural significance using a microbial agent, such as proteins derived from fungi, bacteria, or insects, affords an environmentally friendly and commercially attractive alternative to synthetic chemical pesticides. Generally speaking, the use of biopesticides presents a lower risk of pollution and environmental hazards, and biopesticides provide greater target specificity than is characteristic of traditional broad-spectrum chemical insecticides. In addition, biopesticides often cost less to produce and thus improve economic yield for a wide variety of crops.
Certain species of microorganisms of the genus Bacillus, notably Bacillus thuringiensis and Bacillus papilliae, are known to possess pesticidal activity against a broad range of pests, including insects and nematodes. Pesticidal activity appears to be concentrated in parasporal crystalline protein inclusions, although pesticidal proteins have also been isolated from the vegetative growth stage of Bacillus. Agricultural scientists have developed crop plants with enhanced insect resistance by genetically engineering the plants to produce pesticidal proteins from Bacillus. For example, corn and cotton plants have been genetically engineered to produce pesticidal proteins isolated from strains of B. thuringiensis known as δ-endotoxins or Cry toxins (see, e.g., Aronson (2002) Cell Mol. Life. Sci. 59(3):417-425; Schnepf et al. (1998) Microbiol Mol Biol Rev. 62(3):775-806). These genetically engineered crops are now widely used in American agriculture and have provided the farmer with an environmentally friendly alternative to traditional insect-control methods. Similarly, potatoes genetically engineered to contain pesticidal Cry toxins have been sold to the American farmer.
There remains a need for biopesticides, such as Bt toxins, having nematicidal activity and methods of using such biopesticides to protect crops from plant-parasitic nematodes.